Things for convenient and human-friendly interaction with signed numbers and their parts

This crate has 0 dependencies aside from std (no_std coming soon?).

The crate also includes a small doctest and a criterion benchmark for all of its functions.

``` use signed::Signed;

let mut n: i32 = 42; // A number to test operations with it

let mut absn = n.getabsolute(); // Gets a "pointer" to an absolute value of a number

absn -= &2; drop(absn);

assert_eq!(n, 40);

let mut absn = n.getabsolute(); // Gets a "pointer" to an absolute value of a number

absn += &6; drop(absn);

assert_eq!(n, 46);

n = -42; // Let's try with negative number

// Unfortunately, due to assertions, absn has to be dropped before immutable use, but when n // is changed, absn is changed accordingly

let mut absn = n.getabsolute(); // Gets a "pointer" to an absolute value of a number

absn -= &4; drop(absn);

assert_eq!(n, -38); // Now that's different, we subtracted, but got a number bigger than the initial one.

let mut absn = n.getabsolute(); // Gets a "pointer" to an absolute value of a number

absn += &6; drop(absn);

assert_eq!(n, -44); // And by adding to the absolute value, we get a number smaller.

// All of this works for i8, i16, i32, i64 and i128! ```